JPH1031232A - Guest host liquid crystal display device and manufacturing method thereof - Google Patents

Abstract

[PROBLEMS] To protect a quarter-wave plate layer incorporated in a guest-host liquid crystal display device and to form a high-performance alignment layer. SOLUTION: The guest-host liquid crystal display device includes a pair of substrates 1 and 2 bonded to each other via a predetermined gap and a guest-host liquid crystal 5 held in the gap and containing a dichroic dye 4. On the lower substrate 2, at least a pixel electrode 6, a quarter-wave plate layer 7, and an alignment layer 8 are formed. At least the counter electrode 9 is formed on the upper substrate 1. A pixel is formed between each pixel electrode 6 and the counter electrode 9. The quarter-wave plate layer 7 is made of uniaxially oriented polymer liquid crystal, and is patterned in an island shape in advance according to the shape of the pixel. The pixel electrode 6 is patterned so as to cover the corresponding polymer liquid crystal island, and functions as a guard film. The alignment layer 8 is disposed on the pixel electrode 6 and is formed so as to be isolated from the lower polymer liquid crystal island protected by the pixel electrode 6 and to be in contact with the upper guest host liquid crystal 5 and to keep the same fixed. The orientation is controlled in the direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a guest-host liquid crystal display device and a method of manufacturing the same. More specifically, the present invention relates to a technology for improving the utilization efficiency of incident light by forming a quarter-wave plate layer as a polarization conversion element in a panel. More specifically, the present invention relates to a protection structure and a protection method for a quarter-wave plate layer having poor solvent resistance.

[0002]

2. Description of the Related Art A reflection type guest-host liquid crystal display device having a quarter-wave plate layer built in a panel as a polarization conversion element is known, and is disclosed in, for example, Japanese Patent Application Laid-Open No. Hei 6-222351. As shown in FIG. 5, the guest-host liquid crystal display device 101 includes a pair of upper and lower substrates 102 and 103.
It is assembled using A pair of substrates 102 and 10
Numeral 3 is made of an insulating material such as glass, quartz, plastic, or the like, and at least the upper substrate 102 has transparency. A guest-host liquid crystal 104 including a nematic liquid crystal molecule 104a and a dichroic dye 105 is interposed between the substrates 102 and 103. The dichroic dye 105 is a p-type dye having a transition dipole moment substantially parallel to the long axis of the molecule. Although not shown on the inner surface 102a of the upper substrate 102, a switching element including a two-terminal element such as an MIM or a three-terminal element such as a TFT, and a pixel electrode 106
Are formed. On the inner surface 102a of the upper substrate 102 on which the switching elements and the pixel electrodes 106 are formed,
Further, an alignment layer 107 made of a polyimide resin or the like is formed. The surface of the alignment layer 107 has been subjected to a rubbing process in order to horizontally align the nematic liquid crystal molecules 104a. On the other hand, on the inner surface 103a of the lower substrate 103, a light reflecting layer 108 and a quarter-wave plate layer 109 are formed in this order. The quarter-wave plate layer 109 is made of a uniaxially oriented polymer liquid crystal. This is formed by heating a polymer liquid crystal and attaching it to a separately heated or cooled substrate 103. or,
On the surface of the quarter-wave plate layer 109, a counter electrode 110 and an alignment layer 111 are formed in this order. The alignment layer 111 is made of polyimide resin or the like like the upper alignment layer 107,
The surface is rubbed.

[0005] Next, the operation of the reflective guest-host liquid crystal display device 101 for monochrome display will be briefly described. When no voltage is applied, the liquid crystal molecules 104a are horizontally aligned along the rubbing direction of the upper and lower alignment layers 107 and 111, and the dichroic dye 105 is similarly aligned. When light incident from the upper substrate 102 side passes through the guest-host liquid crystal 104, a component of the incident light having a vibration plane parallel to the major axis direction of the molecules of the dichroic dye 105 becomes a dichroic dye 1
05 is absorbed. Other components having a vibration plane perpendicular to the major axis direction of the molecules of the dichroic dye 105 pass through the guest-host liquid crystal 104 and form a quarter formed on the inner surface 103a of the lower substrate 103. The light is circularly polarized by the one-wavelength plate layer 109 and is reflected by the light reflecting layer 108. At this time, the polarization of the reflected light is reversed, passes through the quarter-wave plate layer 109 again, and is converted into light having a vibration plane parallel to the major axis direction of the molecules of the dichroic dye 105. . Since this light is absorbed by the dichroic dye 105, a substantially complete black display is obtained. On the other hand, when a voltage is applied, the nematic liquid crystal molecules 104
a is oriented vertically along the direction of the electric field, and the dichroic dye 105
Are similarly oriented. Light incident from the upper substrate 102 side passes through the guest-host liquid crystal 104 without being absorbed by the dichroic dye 105, and is reflected by the light reflection layer 108 without being polarized by the quarter-wave plate layer 109. The reflected light passes through the quarter-wave plate layer 109 again and exits without being absorbed by the guest-host liquid crystal 104. Therefore, white display is obtained.

[0004]

In the conventional structure shown in FIG. 5, a uniaxially oriented polymer liquid crystal is used as a quarter-wave plate layer. This polymer liquid crystal has relatively poor solvent resistance,
It easily dissolves or swells in polar solvents and the like and loses uniaxial orientation. Generally, an alignment layer 111 for the guest-host liquid crystal 104 is formed on the quarter-wave plate layer 109. For example, an alignment agent in which a polyimide resin is dissolved in a solvent such as n-methyl-2-pyrrolidone (NMP) or γ-butyrolactone is applied, and the solvent is evaporated to form an alignment layer 111 made of the polyimide resin. In this case, the high-molecular liquid crystal constituting the quarter-wave plate layer 109 may be dissolved in the solvent contained in the alignment agent, and the uniaxial anisotropy may be lost. Therefore, in the conventional structure, there was no alternative but to use a water-soluble alignment agent using polyvinyl alcohol (PVA) as a practical means. However, as shown in FIG. 5, the alignment layer made of PVA can horizontally align the liquid crystal molecules 104a, but cannot vertically align the liquid crystal molecules 104a. From the viewpoint of display quality, the vertical alignment type guest-host liquid crystal display device was not able to be realized in spite of being superior in contrast and the like as compared with the horizontal alignment type guest-host liquid crystal display device. That is, since the choice of the alignment agent is limited due to the solvent resistance of the quarter-wave plate layer, it was difficult to produce a vertical alignment type guest-host liquid crystal display device by a realistic process. .

[0005]

In order to solve the above-mentioned problems of the prior art, the following measures have been taken. That is, the guest-host liquid crystal display device according to the present invention has, as a basic configuration, a pair of substrates joined to each other via a predetermined gap and a guest-host liquid crystal held in the gap and containing a dichroic dye. ing. On one substrate, at least a pixel electrode, a quarter-wave plate layer, and an alignment layer are formed. At least a counter electrode is formed on the other substrate, and a pixel is formed between each pixel electrode and the counter electrode. The quarter-wave plate layer is made of uniaxially oriented polymer liquid crystal, and is patterned in an island shape in advance according to the shape of the pixel.
The pixel electrodes are patterned so as to cover the corresponding polymer liquid crystal islands. The alignment layer is disposed on the pixel electrode and is formed so as to be isolated from the lower polymer liquid crystal island protected by the pixel electrode, and contacts the upper guest host liquid crystal in a predetermined direction. It is characterized in that the orientation is controlled. Preferably, a switching element for driving each pixel electrode and a flattening layer for filling the unevenness are formed on the one substrate. In this case, the quarter-wave plate layer is formed on the flattening layer, and the pixel electrode has a contact hole provided through the flattening layer and the quarter-wave plate layer. Connected to the corresponding switching element via the switch. In such a structure, the quarter-wave plate layer is patterned in an island shape when the contact hole is opened together with the planarizing layer.

The guest-host liquid crystal display device according to the present invention is manufactured by the following steps. First, a quarter-wave plate layer made of a uniaxially oriented polymer liquid crystal is formed on one substrate. Next, the quarter-wave plate layer is patterned in an island shape. Subsequently, pixel electrodes are formed so as to individually cover the patterned islands of the quarter-wave plate layer. Further, an alignment agent is applied on the pixel electrode, and an alignment layer is formed in a state of being isolated from the lower quarter-wave plate layer protected by the pixel electrode. Thereafter, the other substrate on which the counter electrode is formed in advance is bonded to the one substrate via a predetermined gap. Finally, a guest-host liquid crystal containing a dichroic dye is injected into the gap. Thus, a reflective guest-host liquid crystal display device is completed.

In a guest-host liquid crystal display device having a quarter-wave plate layer incorporated therein, an alignment layer made of a polyimide film or the like is used to regulate the alignment of the guest-host liquid crystal. However, many high-molecular liquid crystals (liquid crystal polymers) constituting the quarter-wave plate layer have low solvent resistance and are dissolved in NMP, γ-butyrolactone, or the like, which is a solvent for polyimide. Therefore, in the present invention, a transparent conductive film such as ITO constituting the pixel electrode is used as a guard film (protective film) so that the liquid crystal polymer does not directly contact the alignment agent of the polyimide film. That is, in order to form an alignment layer on the liquid crystal polymer which becomes a quarter-wave plate layer, the liquid crystal polymer is patterned in advance, and ITO is coated on the entire liquid crystal polymer patterned in an island shape and used as a guard film. ing. Since ITO constituting the pixel electrode is used as the guard film, it is possible to form an orientation layer for the guest-host liquid crystal without increasing the number of additional layers and processes.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic partial sectional view showing the structure of a guest-host liquid crystal display device according to the present invention. As shown in the figure, the guest-host liquid crystal display device is assembled using a pair of upper and lower substrates 1 and 2 joined to each other with a predetermined gap. The upper substrate 1 is transparent and located on the incident side, and the lower substrate 2 is not necessarily transparent and is located on the reflecting side. A guest-host liquid crystal 5 containing a nematic liquid crystal molecule 3 and a dichroic dye 4 is held in a gap between the pair of substrates 1 and 2. On the lower substrate 2, at least a pixel electrode 6, a quarter-wave plate layer 7, and an alignment layer 8 are formed. At least the counter electrode 9 and the alignment layer 10 are formed on the upper substrate 1. A pixel is formed between each pixel electrode 6 and the counter electrode 9. The guest host liquid crystal 5 is sandwiched between upper and lower alignment layers 10 and 8, and the nematic liquid crystal molecules 3 are vertically controlled with respect to the substrates 1 and 2 by the alignment ability of the alignment layers 10 and 8. It should be noted that the present invention is not limited to the vertical alignment, but may be a horizontal alignment, but the former is more advantageous than the latter in terms of display quality and the like. In order to realize the vertical alignment of the nematic liquid crystal molecules 3, the upper and lower alignment layers 10, 8 are made of polyimide resin or the like. Alignment layer 1 using an alignment agent obtained by dissolving a polyimide resin in a predetermined organic solvent
0 and 8 are formed.

As a feature, the quarter-wave plate layer 7 is made of uniaxially oriented polymer liquid crystal, and is patterned in an island shape in advance in accordance with the shape of the pixel. The quarter-wave plate layer 7 is uniaxially oriented by using the base alignment layer 11. The pixel electrode 6 is made of a transparent conductive film such as ITO and is patterned so as to cover the corresponding polymer liquid crystal island, and functions as a guard film. The alignment layer 8 is disposed on the pixel electrode 6 and is formed so as to be isolated from the lower polymer liquid crystal island protected by the pixel electrode 6 and to be in contact with the upper guest-host liquid crystal 5 and keep it fixed. The orientation is controlled in the direction. As described above, in the present invention, since the polymer liquid crystal constituting the quarter-wave plate layer 7 is completely covered with the pixel electrode 6, an organic alignment agent obtained by mixing a polyimide and a solvent is applied thereon. The layer 8 can be formed. This makes it possible to control the vertical alignment of the nematic liquid crystal molecules 3 included in the guest-host liquid crystal 5 and improve the display quality of the guest-host liquid crystal display.

This embodiment is of an active matrix type, and a thin film transistor 12 is formed on a substrate 2 as a switching element for driving an individual pixel electrode 6, for example. The thin film transistor 12 is a bottom gate type, and has a structure in which a gate electrode 13, a gate insulating film 14, a semiconductor thin film 15, and a stopper 16 are stacked in order from the bottom. Of course, the present invention is not limited to this, and a thin film transistor having a top gate structure or another active element may be used. The thin film transistor 12 is covered with an interlayer insulating film 17, on which a source electrode 18s and a drain electrode 18d are formed by patterning. A light reflection layer 19 having irregularities is also formed on the interlayer insulating film 17. A flattening layer 20 is formed so as to fill the unevenness of the thin film transistor 12 and the light reflection layer 19. In this case, the quarter-wave plate layer 7 is formed on the flattening layer 20 via the base alignment layer 11. The pixel electrode 6 is connected to the corresponding thin film transistor 1 through a contact hole 21 provided through the flattening layer 20 and the quarter-wave plate layer 7.
2 is connected to the second drain electrode 18d. The quarter-wave plate layer 7 is simultaneously patterned with the planarizing layer 20 in an island shape when the contact hole 21 is opened.

Next, a method for manufacturing a guest-host liquid crystal display device according to the present invention will be described in detail with reference to FIGS. First, in a step (A) of FIG. 2, a thin film transistor 12 having a bottom gate structure is integratedly formed on an insulating substrate 2 made of glass, quartz, or the like. Specifically, a gate insulating film 14 is provided by patterning a gate electrode 13 made of a high melting point metal or the like and then depositing a silicon oxide or silicon nitride by CVD or the like. A semiconductor thin film 15 made of polycrystalline silicon or the like is formed thereon by CVD or the like, and is patterned so as to form an element region of the thin film transistor 12. The stopper 1 is aligned thereon with the gate electrode 12.
6 is formed by patterning. Using the stopper 16 made of an insulator as a mask, impurities are injected into the semiconductor thin film 15 by ion doping or ion implantation to form the thin film transistor 12. The thin film transistor 12 is covered with an interlayer insulating film 17 made of an oxide or a nitride.

In the step (B), a contact hole is opened in the interlayer insulating film 17. An aluminum film or the like is deposited thereon by sputtering or the like, and is patterned into a predetermined shape to form a source electrode 18s and a drain electrode 18d. In this step, the light reflection layer 19 is formed at the same time.
The light reflection layer 19 is composed of a resin film 19a having irregularities and an aluminum film 19b formed on the surface thereof.
The resin film 19a is a photosensitive resin film having irregularities patterned by photolithography. This photosensitive resin film 1
9a is made of, for example, a photoresist, and is applied to the entire surface of the substrate 2. This is exposed through a predetermined mask, and is patterned into, for example, a cylindrical shape. Then, by heating and performing reflow, the uneven shape can be formed stably. An aluminum film 19b having a desired film thickness and good light reflectivity is formed on the surface of the concavo-convex shape thus formed. If the depth dimension of the irregularities is set to several μm, good light scattering characteristics can be obtained, and the light reflection layer 19 exhibits white. The light reflection layer 19 is subdivided corresponding to each pixel, and the aluminum film 19b has the same potential as the drain electrode 18d.

In step (C), the thin film transistor 12
Then, the flattening layer 20 is formed so as to fill the unevenness of the light reflection layer 19. It is preferable to use a transparent organic material such as an acrylic resin for the planarization layer 20. An underlying alignment layer 11 is formed thereon. By interposing the planarization layer 20, the film formation and the rubbing treatment of the base alignment layer 11 can be performed stably. For this reason, a quarter-wave plate layer can be accurately formed on the base alignment layer.
If the flattening layer 20 is not provided, the unevenness of the light reflection layer 19 directly affects the quarter-wave plate layer, and the desired optical characteristics may not be obtained. However, the present invention does not require the planarizing layer 20 as an essential component.

Next, in step (D), a quarter-wave plate layer 7 made of uniaxially oriented polymer liquid crystal is formed on the base alignment layer 11. Specifically, a polymer liquid crystal material is applied on the base alignment layer 11. This polymer liquid crystal is, for example, a side-chain polymer liquid crystal using a benzoate ester mesogen as a pendant. This polymer liquid crystal is mixed with a solution obtained by mixing cyclohexane and methyl ethyl ketone at a ratio of 8 to 2 to 3 to 3.
Dissolve 5% by weight. This solution is spin-coated at a rotation speed of, for example, 1000 rpm to form a polymer liquid crystal on the base alignment layer 11. Thereafter, the substrate is heated, and the polymer liquid crystal is once heated to an optically isotropic state. Subsequently, the heating temperature is gradually lowered to return to a room temperature state through a nematic phase. In the nematic phase, the polymer liquid crystal is
Thus, a desired uniaxial orientation can be obtained by aligning along one rubbing direction. This uniaxial orientation state is fixed by returning the substrate 2 to room temperature. By such an annealing treatment, the liquid crystal molecules contained in the polymer liquid crystal material are uniaxially oriented, and a desired quarter-wave plate layer 7 is obtained.

In step (E) of FIG. 3, a photoresist 7a is applied on the quarter-wave plate layer 7. As the photoresist 7a, a water-soluble photosensitive agent that does not adversely affect the underlying quarter-wave plate layer 7 is used. For example, an aqueous solution (0.1 to 5 wt%) of polyvinyl alcohol (PVA) is spin-coated. At this time, for example, a small amount of ammonium bichromate is added to the aqueous solution to cause a photocrosslinking reaction of PVA.

In step (F), an exposure process is performed using a desired mask (not shown) using a mercury lamp or a xenon lamp. Further, when a washing process is performed, the unexposed portions of the photoresist 7a are dissolved in water, and the photoresist 7a is patterned. As shown, this photoresist 7a is exposed and developed (photolithography).
And the drain electrode 1
The window 7b aligned with 8d is opened.

In step (G), etching is performed using the patterned photoresist 7a as a mask, and a contact hole 21 penetrating the quarter-wave plate layer 7 and the flattening layer 20 is opened. At this time, the quarter-wave plate layer 7 and the flattening layer 20 are simultaneously patterned in an island shape. This etching is performed by, for example, dry etching by irradiating oxygen plasma. Alternatively, wet etching using an organic etching solution for dissolving the quarter-wave plate layer 7 and the planarizing layer 20 may be performed instead of the dry etching method. Thus, the flattening layer 20 and the quarter-wave plate layer 7 are patterned for each pixel.
Since this patterning can be performed at the same time as the contact hole 21 is dug, the process is not particularly increased.

Proceeding to step (H) in FIG. 4, a transparent conductive film made of ITO or the like is formed so as to completely cover the quarter-wave plate layer 7 and the flattening layer 20 patterned in an island shape. .
This transparent conductive film is patterned for each pixel and processed into a pixel electrode 6. The pixel electrode 6 is electrically connected to the drain electrode 18d of the thin film transistor 12 through the contact hole 21 and completely covers the island-shaped quarter-wave plate layer 7 to serve as a guard film.

Proceeding to the step (I), an alignment agent is applied on the pixel electrode 6 and the alignment layer 8 is separated from the lower quarter-wave plate layer 7 protected by the guard film of the pixel electrode 6. To form As the alignment agent, for example, a material obtained by dissolving polyimide in a solvent such as NMP or γ-butyrolactone is used.
In the present invention, since the quarter-wave plate layer 7 having poor solvent resistance is completely covered with the pixel electrode 6, there is no possibility of being damaged by the solvent contained in the alignment agent. Instead of using the pixel electrode 6 as a guard film, a structure in which a protective layer made of a transparent acrylic resin or the like is separately provided between the quarter-wave plate layer 7 and the alignment layer 8 is also conceivable. However, in this structure, the manufacturing process is complicated due to the addition of the protective layer, and the optical characteristics such as the reflectance are deteriorated due to the interposition of the protective layer. In particular, when a protective layer is interposed between the quarter-wave plate layer 7 and the pixel electrode 6, a process of opening a contact hole is also required, resulting in complication. or,
A structure in which a protective layer is interposed between the pixel electrode 6 and the alignment layer 8 is also conceivable. However, in this case, the insulator of the protective layer exists between the counter electrode and the pixel electrode 6, and the operating characteristics of the display device deteriorate. Specifically, the effective voltage applied to the guest-host liquid crystal decreases, and burn-in or the like occurs due to charging, which leads to deterioration in image quality.

Finally, proceeding to the step (J), the counter electrode 9
Then, the upper substrate 1 on which the alignment layer 10 is formed is joined to the lower substrate 2 via a predetermined gap. After this, dichroic dye 4
And a pair of upper and lower substrates 1 and 2
, A reflection type guest-host liquid crystal display device is completed.

[0021]

As described above, according to the present invention, after the quarter-wave plate layer is patterned in the shape of an island, the pixel electrodes are formed so as to individually cover them. Then, an alignment agent is applied on the pixel electrode, and an alignment layer is formed in a state of being isolated from the lower quarter-wave plate layer completely protected by the pixel electrode. With this structure, it is possible to form a non-water-soluble alignment layer such as polyimide on a quarter-wave plate layer having poor solvent resistance without increasing the number of processes and additional protective layers. As a result, the guest-host liquid crystal layer can be vertically aligned, leading to an improvement in display quality, and a highly reliable polyimide or the like can be used as the alignment layer, thereby improving the reliability of the guest-host liquid crystal display device.

[Brief description of the drawings]

FIG. 1 is a schematic partial sectional view showing the structure of a guest-host liquid crystal display device according to the present invention.

FIG. 2 is a process diagram illustrating a method for manufacturing a guest-host liquid crystal display device according to the present invention.

FIG. 3 is a process drawing showing the same manufacturing method.

FIG. 4 is a process drawing showing the same manufacturing method.

FIG. 5 is a sectional view showing an example of a conventional guest-host liquid crystal display device.

[Description of Signs] 1 ... substrate, 2 ... substrate, 3 ... liquid crystal molecule, 4 ... dichroic dye,
5 Guest host liquid crystal, 6 Pixel electrode, 7 Quarter wave plate layer, 8 Alignment layer, 9 Counter electrode, 10 Alignment layer, 1
DESCRIPTION OF SYMBOLS 1 ... Underlying alignment layer, 12 ... Thin film transistor, 18s ... Source electrode, 18d ... Drain electrode, 19 ... Light reflection layer, 2
0: flattening layer, 21: contact hole

Claims (4)

[Claims] 1. A semiconductor device comprising: a pair of substrates joined to each other via a predetermined gap; and a guest-host liquid crystal held in the gap and containing a dichroic dye. A guest-host liquid crystal display device in which one wavelength plate layer and an alignment layer are formed, at least a counter electrode is formed on the other substrate, and pixels are formed between individual pixel electrodes and the counter electrode, The quarter-wave plate layer is made of uniaxially oriented polymer liquid crystal and is patterned in advance in an island shape according to the shape of the pixel, and the pixel electrode is patterned so as to cover the corresponding polymer liquid crystal island. The alignment layer is disposed on the pixel electrode, is formed separately from the lower polymer liquid crystal island protected by the pixel electrode, and is in contact with the upper guest host liquid crystal. In a certain direction A guest-host liquid crystal display device which controls alignment. 2. A switching element for driving an individual pixel electrode and a flattening layer filling the unevenness are formed on the one substrate, and the quarter-wave plate layer is formed on the flattening layer. Wherein the pixel electrode is connected to a corresponding switching element through a contact hole provided through the flattening layer and the quarter-wave plate layer. 2. The guest-host liquid crystal display device according to 1. 3. The guest-host liquid crystal display device according to claim 2, wherein the quarter-wave plate layer is patterned in an island shape when opening a contact hole together with the planarizing layer. 4. A step of forming a quarter-wave plate layer made of uniaxially oriented polymer liquid crystal on one of the substrates, a step of patterning the quarter-wave plate layer in an island shape, Forming a pixel electrode so as to individually cover the islands of the quarter-wave plate layer, and applying an alignment agent on the pixel electrode to protect the lower quarter protected by the pixel electrode. A step of forming an alignment layer in a state separated from the wavelength plate layer; a step of bonding the other substrate on which the counter electrode is formed in advance to the one substrate via a predetermined gap; and a step of containing a dichroic dye. Injecting a guest-host liquid crystal into the gap.